This invention relates in general to refrigeration systems. In particular, this invention relates to an improved refrigeration system that includes an expansion device having a microvalve.
MEMS (Micro Electro Mechanical Systems) are a class of systems that are physically small, having features with sizes in the micrometer range; i.e., about 10 μm or smaller. These systems have both electrical and mechanical components. The term “micromachining” is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today, there are many more micromachining techniques and materials available. The term “micromachined device” as used in this application means a device having some features with sizes of about 10 μm or smaller, and thus by definition is at least partially formed by micromachining. More particularly, the term “microvalve” as used in this application means a valve having features with sizes of about 10 μm or smaller, and thus by definition is at least partially formed by micromachining. The term “microvalve device” as used in this application means a micromachined device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or standard sized (larger) components. Similarly, a micromachined device may include both micromachined components and standard sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve component movably supported by a body for movement between a closed position and a fully open position. When placed in the closed position, the valve component substantially blocks or closes a first fluid port that is otherwise in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve component moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
U.S. Pat. Nos. 6,523,560; 6,540,203; and 6,845,962, the disclosures of which are incorporated herein by reference, describe microvalves made of multiple layers of material. The multiple layers are micromachined and bonded together to form a microvalve body and the various microvalve components contained therein, including an intermediate mechanical layer containing the movable parts of the microvalve. The movable parts are formed by removing material from an intermediate mechanical layer (by known micromachined device fabrication techniques, such as, but not limited to, Deep Reactive Ion Etching) to create a movable valve element that remains attached to the rest of the part by a spring-like member. Typically, the material is removed by creating a pattern of slots through the material to achieve the desired shape. The movable valve element will then be able to move in one or more directions an amount roughly equal to the slot width.
U.S. Pat. No. 7,156,365 the disclosure of which is also incorporated herein by reference, describes a method of controlling the actuator of a microvalve. In the disclosed method, a controller supplies an initial voltage to the actuator which is effective to actuate the microvalve. Then, the controller provides a pulsed voltage to the actuator which is effective to continue the actuation of the microvalve.
Refrigeration is frequently accomplished by continuously circulating, evaporating, and condensing a fixed supply of a refrigerant throughout a closed system. Evaporation occurs at a relatively low temperature and low pressure, while condensation occurs at a relatively high temperature and high pressure. Thus, refrigeration systems can function to transfer heat from an area of low temperature (such as, for example, an interior of a refrigerator) to an area of high temperature (such as, for example, a kitchen in which the refrigerator is located).
One common type of refrigeration system is often referred to as a fixed orifice refrigeration system. In a fixed orifice refrigeration system, refrigerant from the condenser is passed through an expansion device including an orifice having a fixed size. The size of this fixed orifice is usually selected in accordance with the anticipated normal operating conditions of the refrigeration system. One well known type of fixed orifice expansion device is a capillary tube, which is usually embodied as an elongated hollow cylindrical tube having a predetermined length and interior passageway having a predetermined size. Capillary tube types of expansion devices are desirable because they are very simple and inexpensive.
As mentioned above, known capillary tubes have an orifice that is fixed in size, and that size is typically determined in accordance with the anticipated normal operating conditions of the refrigeration system. However, when operated under certain transient conditions (such as where the cooling load demand on increased relatively rapidly), a fixed orifice type of refrigeration system may operate in a less than optimal manner. As a result, it may take an undesirably long amount of time for the fixed orifice type of refrigeration system to achieve a desired target refrigeration temperature. A few examples of transient conditions include when: (1) a new refrigerator installed and turned on the first time; (2) one or more warm products are placed in a refrigerator; (3) a refrigerator door is opened and closed during use; and (4) a refrigerator door is accidentally left open (or at least not fully closed) for an extended period of time. Thus, it would be desirable to provide an improved structure for a refrigeration system that is readily adaptable in response to one or more transient conditions so as to continuously operate in an optimal manner in spite of such transient conditions, yet remains relatively simple and inexpensive.